1. Field of the Invention
The present invention relates to a liquid supply method and a liquid supply apparatus for supplying a liquid, e.g., a polishing liquid for use in a polishing section of CMP or a processing liquid for use in a semiconductor fabrication apparatus, to a predetermined liquid-supply area. The present invention also relates to a substrate polishing apparatus using such a liquid supply apparatus, and a method of measuring a supply flow rate of a liquid.
2. Description of the Related Art
A conventional liquid supply apparatus of this type is disclosed in Japanese laid-open patent publication 11-126764, and FIG. 1 shows a structure of this type of apparatus. Hereinafter, a polishing liquid supply apparatus shown in FIG. 1 for supplying a mixture of slurry and pure water will be described. A polishing liquid supply apparatus 200 includes an injector (pump) 201, a self-control valve (constant-pressure valve) 202, a flow sensor 203, an orifice 204, and a controller 205. Pressurized air (at 0.3 MPa) is supplied alternately to supply ports of the injector 201 so as to increase pressure of slurry 207 or pure water 208 to a controllable level. The flow sensor 203 detects a flow rate of a liquid and sends a signal S thereof to the controller 205. This controller 205 adjusts pressure of air 209, which is to be supplied to the self-control valve 202, so that the flow rate of the liquid reaches a value that is preset in the controller 205. With this structure, a polishing liquid 210 is supplied to a polishing surface of a polishing table at the flow rate that is preset in the controller 205. The self-control valve 202 uses the orifice 204 for controlling the flow rate, and the flow sensor 203 has a differential pressure type orifice 203a therein.
The above-described polishing liquid supply apparatus 200 has several problems as follows:
(1) Since the orifice 204 is located downwardly (downstream) of the flow sensor 203, this orifice 204 could become clogged with the slurry 207. Even if the orifice 204 is not clogged, the slurry 207 is attached to the orifice 204, thus narrowing a path. If the path is narrower than is required, the flow rate cannot be controlled.
(2) Since the flow sensor 203 is a differential pressure type sensor having the orifice 203a therein, the same problems as described in (1) would arise.
(3) When flow of the liquid is suddenly changed by the orifices 203a and 204, the liquid is stressed. Depending on the type of liquid, such stress would change a property of the liquid, such as coagulation, exerting an influence on processing.